The present invention relates to tools for use in surgically installing apparatus for correcting orthopedic deformities in a patient and, in particular, to tools specifically designed to facilitate installation of a spinal osteosynthesis system in a patent utilizing a unique set screw having a break-off head.
Spinal osteosynthesis apparatus generally comprise a rod or system of rods which are secured along at least a portion of the spine by bone screws, including sacral screws and pedicle screws, transverse connectors and bone hooks for stabilizing and adjusting spinal alignment. The bone screws, transverse connectors, bone hooks and related items which are intended for use in connecting the rods to the bone and to facilitate adjustment of the rods may collectively be referred to as hardware or implants. In a very basic apparatus, the bone screws have a spinal rod receiving bore extending through a ring or head of the screw. The screws are secured in the vertebra at desired locations and a spinal rod is then extended through the spinal rod bore in each bone screw. Set screws, inserted in threaded bores extending through the wall of the screw ring, preferably perpendicular to the axis of the spinal rod bore, are tightened to fix the translational and rotational relationship of the rods within the bores. The rods may then be bent or formed to support the spine in a desired manner or to exert the desired corrective or stabilizing forces on the spine.
A slightly more complicated system uses transverse connectors in association with the bone screws to secure the spinal rods. The transverse connectors include an arm and a head. The head has a spinal rod bore extending therethrough and the arm is normally equivalent in diameter to the spinal rod. The arm of the connector is inserted through the spinal rod bore in the pedicle screw then the spinal rod may be inserted through the spinal rod bore in the transverse connectors. A threaded bore extends through the head of the connector perpendicular to the axis of the spinal rod bore. Once the rod is inserted through the bore in the transverse connectors the set screws are inserted through the threaded bores and tightened to fix the relative position of the rod within the spinal rod bore and set screws are inserted in the threaded bores and tightened to fix the position of the transverse connector with respect to the pedicle screws.
The pedicle screws, transverse connectors, bone hooks or related implants or hardware may be of the closed end type as discussed above or of an open end type wherein the head of the screw or connector generally incorporates a U-shaped channel or groove, an upper end of which may be closed off by a cap or saddle to form the spinal rod bore. The threaded set screw bore typically extends through the cap. With open end type implants, the spinal rod may be inserted from above, into the U-shaped channel instead of having to insert the spinal rod axially through the rod receiving bores of closed end type implants.
A preferable aspect of any osteosynthesis apparatus is to provide a system wherein the components may be readily manipulated to facilitate relatively easy and rapid installment or disassembly. Manipulation of small headed set screws provides a significant challenge to surgeons installing currently available systems, especially when working in the close confines of an operative site. Some techniques require the surgeon to operate through an opening that is just sufficient in size to receive the parts of the apparatus to be assembled and the tools with no room provided for the surgeon's hands or fingers. Due to the nature of use of the set screw, it is important that the set screw be relatively small to reduce impact on the patient and irritation caused by the screw. The small size of set screws often makes them difficult to grasp and manipulate.
Currently, set screws are being used in which the head of the screw breaks off or shears off after insertion such that generally no or only a small portion of the set screw extends above or beyond the threaded bore into which it is inserted. The broken off head should be readily captured and removed from the site of the operation. There is a need for a set of tools for installing osteosynthesis apparatus incorporating set screws with break off heads in which the tools facilitate manipulation of the set screws and implants utilizing such set screws and removal of the heads after break-off.